1. Field of the Invention
This invention relates to an image input apparatus, and more particularly to an improvement in means for modifying the exposure thereof.
2. Description of the Prior Art
In a conventional image input apparatus having a lens unit and a photoelectric conversion means, modification of exposure is performed by manually adjusting the iris of the lens unit.
However, since this kind of the apparatus is of manual adjustment, its operation is troublesome, its accuracy is poor, and there is a posibility of producing a deflection of the image due to vibration; thus is desirable to provide an automatic exposure mechanism.
However, because then nature of image originals may cover an extremely large variety, e.g., letters, picture tones, photographic tones, or black and white, color and the like, it is actually extremely difficult to provide a proper exposure with the naked eye for all of these originals, and it becomes necessary to perform some degree of exposure correction.
In such a case, as for the adjutment operation, a method can be considered wherein an iris is opened or closed step by step by a motor with the aid of, for example, a button and the like. However, this method is extremely troublesome, since a reverse operation with regard to the correction operation described above must be repeated when the correction value is returned to the original standard value of the automatic exposure mechanism.